Electrochemical gas detection device

Abstract

An output of a direct current power supply is divided with a pair of resistors, and applied to any of electrodes of an electrochemical gas sensor provided with a detection electrode, a counter electrode and a solid electrolyte membrane through a buffer amplifier. Impedance of the gas sensor is measured by switching with a switch the connection destination of one electrode of the electrochemical gas sensor between a current amplification circuit and an impedance measurement circuit. The impedance measurement circuit is formed of an alternating current power supply that switches a potential of a resistor on a side of one end connected to the switch and a potential on a side of the other end of the resistor, between the output potential and the ground potential of the direct current power supply. Gas concentration is determined by storing humidity dependency and temperature dependency of the electrochemical gas sensor, and correcting the output of the current amplification circuit based on measured impedance and ambient temperature.

1 . An electrochemical gas detection device for detecting a gas by correcting an output of an electrochemical gas sensor, with no reservoir being provided and with the correction being performed in accordance with impedance of the gas sensor,
 the electrochemical gas detection device comprising:   a direct current power supply;   at least one pair of resistors connected to the direct current power supply;   a buffer amplifier outputting a potential following a potential between at least the one pair of resistors;   an electrochemical gas sensor provided with a detection electrode, a counter electrode and a solid electrolyte membrane; with one of the detection electrode and the counter electrode being connected to the buffer amplifier while no reservoir being provided to this gas sensor;   a current amplification circuit for amplifying current flowing through the electrochemical gas sensor,   an impedance measurement circuit for measuring impedance of the electrochemical gas sensor,   a switch for switching the connection destination of one of the electrodes of the electrochemical gas sensor between the current amplification circuit and the impedance measurement circuit;   storage means for storing data on impedance dependency and temperature dependency of the current passing through the electrochemical gas sensor;   a temperature sensor for measuring ambient temperature; and   a microcomputer for reading out data from the storage means in accordance with an output signal of the impedance measurement circuit and an output signal of the temperature sensor, and by correcting the output signal of the current amplification circuit on the basis of the data, determining gas concentration and controlling the switch,   the impedance measurement circuit being formed of: an alternating current power supply for switching a potential of a resistor on a side of one end connected to the switch and a potential on a side of the other end of the resistor, between the output potential and the ground potential of the direct current power supply; and an alternating current voltage measurement circuit for measuring alternating current voltage applied to the electrochemical gas sensor.   
     
     
         2 . The electrochemical gas sensor according to  claim 1 , the alternating current power supply being an output port of the microcomputer. 
     
     
         3 . The electrochemical gas sensor according to  claim 2 , the alternating current voltage measurement circuit being an AD converter of the microcomputer. 
     
     
         4 . The electrochemical gas sensor according to  claim 3 , the output of the alternating current power supply being a rectangular wave.